In telecommunications, white spaces refer to frequencies allocated to broadcasting services but not used locally. National and international bodies assign bands for specific uses, and in most cases, license the rights to the spectrum. This frequency allocation process creates a band plan, in which guard bands may be assigned between used radio bands or channels to avoid interference. In addition, there may be unused portions of radio spectrum that have either never been used or are becoming available as a result of technical changes. In particular, the switchover to digital television has freed up frequency spectrum between 50 MHz and 700 MHz because digital transmissions can be packed into adjacent channels while analog transmissions cannot. Consequently, the band can be compressed into fewer channels, while still allowing for more transmissions. This spectrum made available by the conversion to digital television is sometimes called “digital dividend.”
In the United States, the Federal Communications Commission (FCC) ruled that unlicensed devices guaranteeing that they will not interfere with assigned broadcasts can use the empty white spaces in the frequency spectrum. The abandoned television frequencies (digital dividend) are primarily in the upper UHF 700-megahertz band, covering TV channels 52 to 69 (698 to 806 MHz). Spectrum for television transmission and its white spaces continue to exist below the digital dividend in the UHF band as well as in the VHF band for which mobile users and white-space devices require larger antennas.
A device intended to use these available channels is often referred as a white space device (WSD). A white space device may be designed to detect the presence of existing signals from TV stations and other wireless users to avoid inadvertent use of these channels. Some approaches propose including geo-location capabilities and access to a database indicating channels not used by all TV stations in an area.
Various proposals, including IEEE 802.22 and those from the White Spaces Coalition, have advocated using white spaces left by the termination of analog TV to provide wireless broadband Internet access. However, these efforts may impact wireless microphones, medical telemetry, and other technologies that have historically relied on these open frequencies.
The White Spaces Coalition includes a number of large technology companies that plan to deliver high speed broadband internet access to consumers in the United States via existing white space in unused television frequencies between 54-698 MHz (TV Channels 2-51). One of the goals is to provide data rates of at least 80 Mbps for white space short-range networking.